a. Field of the Invention
The present invention relates generally to methods and apparatus for locating a patient's fossa ovalis in the atrium of a human heart, creating a virtual fossa ovalis using an electroanatomical mapping system and using the information to perform transseptal punctures. In particular, these methods and apparatus may be based, at least in part, on anatomical measurements.
b. Background Art
Transseptal puncture refers to needle puncture of the interatrial septum through the fossa ovalis and is the standard technique for percutaneous introduction of catheters into the left atrium. The technique was described simultaneously by Ross and Cope in 1959. Brockenbrough and colleagues modified the design of the needle and guiding catheter apparatus in the 1960s. The development of selective coronary angiography in the 1960s led to a refinement of catheterization of the left side of the heart using the retrograde approach. This development, along with the occurrence of complications from the transseptal puncture technique led to a decline in the use of the puncture technique. The development of balloon mitral valvuloplasty as well as catheter ablation of arrhythmias arising from the left atrium (or utilizing left sided bypass tracts) has led to a rapid increase in the use of the technique in recent years.
The goal of the transseptal puncture procedure is to cross from the right atrium to the left atrium through the fossa ovalis. In about 25% of the normal population, the fossa ovalis (the septum primum) has not fused to the rest of the interatrial septum (the septum secundum) and therefore a patent foramen ovale is present. In the rest of the population, access to the left atrium requires a mechanical puncture of this area with a needle and catheter combination.
The danger of the transseptal puncture technique lies in the potential development of complications which can be serious and life-threatening. These include perforation of adjacent structures such as the aorta, the coronary sinus or the free wall of the atrium resulting in cardiac tamponade and death. In the Cooperative Study on Cardiac Catheterization in 1968, 0.2% mortality, 6% major complications, and a 3.4% incidence of serious complications were reported, including 43 perforations. Concern over the potentially grave complications has given the procedure an aura of “danger and intrigue.” The complications almost always are due to unintentional puncture of the wrong structure. Therefore, the key to avoiding complications is the correct identification of the fossa ovalis, and accurately directing the needle and catheter through the structure. It is believed that some of the procedure-related complications may be due to insufficient anatomical landmarks and individual variations in the position of the heart with respect to the chest wall.
Transseptal puncture is conventionally performed with X-ray guidance (fluoroscopy). However, fluoroscopy has significant limitations. At best, it provides a shadow of the outer borders of the heart in a single plane and does not identify the intracardiac endocardial structures. Due to the limitations of fluoroscopy and the potential for life threatening complications during transseptal puncture, single plane fluoroscopy alone is not enough. Therefore, more tools have been developed to identify the intracardiac structures. These include: biplane fluoroscopy; use of a pig-tailed catheter to identify the aortic root; pressure manometry to identify aortic/right atrial and left atrial pressures; contrast infusion; and transesophageal (TEE) and intracardiac (ICE) echocardiography.
Biplane fluoroscopy is considered to be expensive and many institutions cannot afford to install such a system in their laboratories. The use of intracardiac (ICE) and transesophageal (TEE) echocardiography to guide the procedure has found increasing popularity in recent years. However, echocardiography also has limitations. The tenting of the fossa ovalis membrane by the transseptal needle visualized by intracardiac echocardiography that one looks for prior to making the puncture may be missed depending on the portion of membrane cut by ultrasound beam. If a different portion of the membrane is tented by the dilator tip, this may not be apparent on the ultrasound picture.
If TEE is used to guide the puncture, a different operator has to operate the TEE system and therefore errors can occur, especially in the interpretation of the data. For example, a different catheter other than the transseptal dilator may be tenting the fossa membrane. In fact, cardiac tamponade and other serious complications can still occur during transseptal puncture, despite the use of ultrasound guidance. In addition, the placement and use of ultrasound catheters requires the insertion of large intravascular sheaths. The additional time and expense of using ultrasound catheters is considerable and routine use of these is impractical.
In summary, the above-described techniques have significant limitations & shortcomings. Thus, there was a need for additional methods and apparatus that assist in identifying the fossa ovalis and which are “user friendly.”
In light of this, Applicant has previously developed apparatus and methods for locating the fossa ovalis and performing transseptal punctures, as described in Applicant's U.S. patent application Ser. No. 10/648,844, filed Aug. 25, 2003 (“the '844 Application,” which is incorporated herein by way of reference). The '844 Application describes, among other things, a transseptal apparatus which incorporates electrodes in the dilator tip, as shown in FIG. 1 herein (and FIG. 7 of the '844 Application). In particular, the incorporation of a “tip” and a “ring” electrode into the dilator tip of the transseptal apparatus allows the measurement of electrophysiological properties of the interatrial septum as the dilator tip is dragged down from the superior vena cava. The fossa ovalis may be identified by the presence of low voltage unipolar and bipolar electrograms that are also wider and fractionated as compared to the rest of the interatrial septum. Other identifying properties may include, for example, a lower slew rate, a higher pacing threshold and a lower impedance.